Reactors such as chemical reactors and heat exchangers are widely used to promote heat transfer, mass transfer and/or chemical reaction rates. In the case of reactors such as chemical reactors, there is often a need to transfer heat into the reactor (e.g., for endothermic reactions) or to transfer heat from the reactor (e.g., exothermic reactions). In commercial practice, in order to achieve economies of scale, it is desirable to use reactors having large diameters. A high heat transfer coefficient within the reactor is desirable in order to promote transfers of heat between the reactor contents and the environment. A high heat transfer coefficient within the reactor is especially desirable near the outside diameter of the reactor, where the ratio of surface area for radial heat flux to the internal volume is lowest and where the amount of heat to be transferred radially is proportional to the volume internal to the source of the reactor. Friction between fluids and the reactor wall often results in relatively low velocities and accordingly relatively lower heat transfer coefficients near the reactor wall where higher heat transfer coefficients are most desirable.
In the case of fixed bed, heterogeneous and catalytic reactors, heat transfer into the reactor wall may limit the reaction rate for endothermic reactions or heat transfer from the reactor may limit the control or safe operation for exothermic reactions. In general, it is desirable to limit the number of internal walls within the reactor to accordingly minimize the number of boundary layers of low velocity and low heat transfer coefficient that heat must pass through in the radial direction. Higher surface area in catalytic reactors provides greater opportunity for acceleration of reactions by providing more sites for catalyst to be effectively deployed. In particular, high geometric surface area near the wall of catalytic reactors increases the available heat for conducting exothermic reactions and the heat sink for endothermic reactions at short distances for heat to travel out of or into the reactors, respectively.